1. Field of the Invention
The present invention relates to a fuel tank structure which is made of resin materials, and which has a pair of interference sections for suppressing deformation of a fuel tank at the time of application of negative pressure of a specified value or higher, provided at the upper surface of the tank and the lower surface of the tank.
2. Description of the Related Art
Recently, fuel tanks formed of resin molding are often used mainly from viewpoint of reduction of weight. However, these types of resin-made fuel tanks are generally lower in rigidity as compared with fuel tanks formed of metal materials, and therefore, a technique has been hitherto adopted in which portions called “stand-off” for assuring rigidity or retaining its shape are added at proper positions of the fuel tank.
For example, Japanese Utility Model Application Laid-Open (JP-U) No. 63-67328 discloses a structure of disposing conical trapezoid stand-offs face to face at a specific interval inward in the tank from the upper surface and the lower surface of the fuel tank.
However, in structures disclosed in JP-U No. 63-67328 and Japanese Patent Application Laid-Open (JP-A) No. 2004-203199, if negative pressure is applied to the fuel tank and the fuel tank is deformed, the upper and lower stand-offs may not contact each other as intended (and therefore, the effect of suppressing deformation due to negative pressure may not be expressed sufficiently). More specifically, generally, since the shape of a resin-made fuel tank is complicated, deformation modes of the upper and lower surfaces of the fuel tank due to negative pressure are varied. Hence, deviation may occur in the displacement direction of the upper and lower stand-offs, and depending on the mode of deformation of the upper and lower surfaces of the fuel tank, the upper and lower stand-offs may not contact each other as designed.
These problems may be solved by using a so-called contact type stand-off, such that the bottoms of the upper and lower stand-offs are shared and integrated, or by expanding the areas of the bottoms of the upper and lower stand-offs. However, the volume occupied by the stand-offs is increased, and the capacity of the fuel tank is sacrificed.